A261617 Numbers n such that n!!! + 3^n is prime.

0, 2, 16, 17, 20, 22, 28, 31, 37, 40, 53, 65, 71, 73, 82, 124, 130, 187, 203, 266, 308, 326, 386, 502, 662, 1919, 3136, 3229, 4640, 8113, 8659, 12307, 20972, 26408, 49391

Offset

1,2

Comments

n!!! is the triple factorial sometimes written n!3.

a(36) > 50000.

Links

Table of n, a(n) for n=1..35.

Example

2 is in the sequence because 2!!!+3^2 = 2+9 = 11 is prime.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 3] + 3^#] &]

Crossrefs

Cf. A007661, A124248, A124249, A261316.

Sequence in context: A138761 A087970 A247634 * A075376 A032935 A004831

Adjacent sequences: A261614 A261615 A261616 * A261618 A261619 A261620

Keyword

nonn

Author

Robert Price, Sep 09 2015

Status

approved